The invention relates to a ringer which is compact and provides a ring signal from a relatively low battery voltage source.
One-piece telephones and cordless telephones require small, inexpensive ringers. One-piece telephones are known which use piezo-ceramic disk type ringers. These ringers require a high voltage to operate effectively and are relatively large in diameter. The piezo-ceramic approach requires a large area, generally 40 millimeters or greater to implement. The acoustic output power is lower than desirable, due to insufficient battery voltage available from most cordless handsets, which commonly employ 3.9 volts direct current (DC) batteries. These ringers also tend to emit a high frequency sound which is very shrill and annoying, and are very susceptible to electromagnetic interference. Cordless telephones are known which use an earpiece transducer or speaker to emit the ring signal. However, such telephones have raised concern for possible accidental hearing loss to users. The speaker approach, whether or not used in the earpiece, is costly and requires a considerable volume in both area and depth to implement. Interface drivers and expensive tooling of case parts are required.
The U.S. Food and Drug Administration has recommended reducing the sound level from the earpiece of cordless phones to such a low level that the effectiveness of the ringer is substantially diminished. A separate ringer is now needed in cordless telephones to emit both a safe and loud sound. Size and power considerations are major limitations in known designs.